Implants have been provided in the past to try to help stabilize the fragments in order to allow the calcaneus to fuse, and more recently these attempts have provided fairly robust plates that can be used for reduction of the bone fragments and further which allow for relatively quick use of the injured limb through the support of the implant. For some situations, these plates remain ideal; however, these prior art plates require a large and relatively invasive surgery and displacement of sensitive soft tissue to access the bone. The implant of the present invention is designed for implantation in appropriate cases through a small incision inferior to the lateral malleolus where the posterior end of the implant can be slipped into position using a drill targeting guide that is spaced an appropriate distance in an offset parallel position from about 0.5 to about 3 inches) from and parallel to the implant so that it can be used like a handle to slip the plate into position adjacent the calcaneus. The relationship between the drill targeting guide and the implant is created and maintained by one of more individual drill guide column assembly, which interlock into one or more selected screw holes of the implant and form a spaced relationship between the implant and a drill targeting guide. Cannulated drill guide sleeves lock in a position in the drill targeting guide and engage other screw holes in the implant (e.g. through minimal incisions or through the skin) to allow for pilot holes to be drilled for ultimate placement of a fastening screw.
Thus, the present invention provides several aspects, which include a novel implant (or plate design), a drill guide assembly, and a method of enabling or performing a hindfoot surgery.
The implant comprises a fully contoured plate which has a ribbon shape (as used herein to mean that the plate is elongate although curving along a length of screw holes, and has a generally uniform width that accommodates the diameter of the screw holes, and further is advantageously diminished somewhat between the holes) with a taper at one end. The plate further has an undulating profile which can be envisioned as an anterior tab having a superior and anterior locking hole and relative to the first hole, an inferior and posterior locking hole which provide for multiplanar fixation. Next, there is a gently s-shaped section having a plurality of locking holes (preferably four) where the profile of the plate section accommodates and supports the posterior facet, The third section of the plate can be based on a series of aligned locking holes that form a linear posterior tab having two to five, and preferably three spaced holes. This blade shaped section of the plate is the posterior section that can be slipped into position adjacent the calcaneus through a small incision inferior to the lateral malleolus. The plate has a bottom surface that faces the bone which includes radiused sections corresponding to the profile sections described above. The anterior tab is curved inferior to superior in a shape which is close to cylindrical and which approximates the shape of the anterior process of the calcaneus. The second section is curved about a different axis so that the plate appears to wrap in the superior direction where it supports the posterior facet. The third portion, i.e. the posterior blade curves about an axis that intersects the screw holes so as to form a portion of a cylinder.
The intermediate portion of the plate includes four locking holes which are internally threaded and are designed to directly support the subtalar joint fragment, specifically just inferior to the posterior facet (i.e. the articulating surface) of the calcaneus. Optionally, the plate further includes smaller holes which allow the use of K wires both for reduction of the fragments, and for further fixation.
In addition, while both the bone facing surface and the outwardly facing surface of the plate are smooth and uninterrupted (other than by the fixation holes) the intermediate portion has an area of increased thickness to provide a reinforced portion in the vicinity of the posterior facet. This area is where the majority of the weight transfer from the tibia to the talus to calcaneus occurs. The plate is provided in a right and a left version and is generally used on the lateral portion of the calcaneal bone situated slightly posterior to the cuboid slightly inferior to the posterior facet, and supported on the posterior portion of the calcaneus. The plate is also provided in multiple profiles for small and large patients.
As a further aspect, the invention relates to a drill guide assembly that includes a flat (i.e. planar) targeting guide which mimics the profile or outline of the plate and is provided with through holes that accept drill columns to connect the targeting guide and the plate. These “drill columns” comprise drill column assemblies which have a top and a bottom that assemble through a hole in the targeting guide to lock the targeting guide intermediate the drill column assembly, drill assembly columns which are single units that lock into the implant and support the targeting guide in a defined relationship, drill sleeves that are held and preferably locked into the targeting guide and are cannulated for insertion of drills, screws or other appropriately sized drill guides. At least one of the drill columns have an end that can be secured in a locking hole of the plate, for example by providing threads that mate with the threaded locking hole of the plate. Further, the external surface of this drill column assembly includes means to secure the targeting guide at a fixed distance from the plate, for example, by providing the external surface of the drill column with a shoulder that forms a flange on which the bottom surface of the targeting guide will rest. An internally threaded sleeve can then be secured over the drill column and screwed onto external threads on the drill column to lock the targeting guide on the drill column so that it will not move. Preferably a second drill assembly column is used to secure this relationship which allows the targeting guide to be used like a handle so that a tapered end of the implant can be slipped into a minimal incision for positioning adjacent the relevant bone surface.